1. Field of the Invention
The present general inventive concept relates to a virtual sound generation system, and more particularly, to an apparatus and method of reproducing a virtual sound of two channels which adaptively reproduces a 2-channel stereo sound signal reproduced through a recording medium such as DVD, CD, or MP3 player etc., based on a listener's position.
2. Description of the Related Art
In general, a virtual sound reproduction system provides a surround sound effect such as a 5.1 channel system, using only two speakers.
Technology related to this virtual sound generation is disclosed in WO 99/49574 (PCT/AU 99/00002, filed on 6 Jan. 1999, entitled, “AUDIO SIGNAL PROCESSING METHOD AND APPARATUS”).
In a conventional virtual sound generation system, a multi-channel audio signal is down-mixed as a 2-channel audio signal using a head related transfer function (HRTF).
Referring to FIG. 1, a 5.1-channel audio signal is input. 5.1-channel includes a left front channel, a right front channel, a center front channel, a left surround channel, a right surround channel, and a low frequency effect (LFE) channel. Left and right impulse response functions are applied to the respective channels. Thus, a corresponding left front impulse response function 4 is convolved with a left front signal 3 with respect to a left front channel 2. The left front impulse response function 4 is an ideal spike output from a left front channel speaker located in an ideal position, and uses an HRTF as an impulse response to be received by a listener's left ear. An output signal 7 is combined with a left channel signal 10 for a headphone. Similarly, a corresponding impulse response function 5 with respect to a right ear for a right channel speaker is convolved with a left front signal 3 so as to generate an output signal 9 to be combined with a right channel signal 11. Thus, the arrangement of FIG. 2 requires about 12 convolution steps with respect to 5.1-channel signals. As such, the 5.1-channel signals are down-mixed by combining a measured HRTF, and even though they are reproduced as 2-channel signals, a surround effect as being reproduced by a multi-channel can be illustrated.
However, in the conventional virtual sound reproduction system, since a sweet spot (i.e., the ideal spot to maximize stereo-sound quality) is defined as a partial region (in general, a center point between two speakers), if a listener does not contact the sweet spot, a stereo surround-sound feeling is remarkably reduced. When the conventional virtual sound reproduction system is used in a TV, a surround-sound stereo feeling cannot be provided to a TV audience in a position that is deviated from the center point between two speakers.